This invention relates generally to optical modulators. More specifically, this invention relates to a method and apparatus for modulating electromagnetic radiation, in particular, a visible or invisible beam of light, in order to transmit information.
Optical communication uses the transmission of electromagnetic waves in the ultraviolet, visible, or infrared regions of the spectrum. Information is applied to the transmission by modulation of the electromagnetic waves. There are many techniques for light modulation as practiced in the prior art. A corner cube reflector of the prior art is depicted in FIG. 1. It contains three mutually orthogonal plano-reflective surfaces 11, 12, and 13, which cumulatively form a right-angle concave mirror. It is well-known in the art that an incident light ray upon the corner cube reflector from direction −A will be reflected back in direction A, i.e., toward the source, if it reflects off its three plano-reflective surfaces 11, 12, and 13. Under certain conditions, an incident light ray may also be reflected back to its source after reflecting off even one or two of its plano-reflective surfaces. For miniaturized corner cube reflectors, i.e., when the size of the light beam is comparable to the size of the corner cube reflector, similar 16 conditions exist although the effective area of the corner cube reflector changes depending on the incident angle as reported by Chu, et. al., “Optical Communication Using Micro Corner Cube Reflectors,” 11th IEEE International Workshop on Micro Electro Mechanical Systems, pp. 1-6 (1997). Chu, et. al., further report that modulation of the reflected light beam can be achieved by providing a movable base mirror as depicted in FIG. 2. FIG. 2 schematically depicts a micro-corner cube reflector 20 of the prior art with movable base mirror 24. The fabrication steps are, however, challenging to achieve release of the base cantilever beam, alignment and planarity of the base mirror 24. Furthermore, microelectromechanical systems (MEMS) similar to that described by Chu, et. al., require hermetic packaging to avoid stiction and other reliability problems. Therefore, while corner cube reflectors show promise as optical modulators, there is a need for improved structures that simplify fabrication, avoid operational problems, mitigate packaging constraints, and improve reliability.